WASHINGTON (AP) — The family of an ex-Marine detained in Iran wants Secretary of State John Kerry to step in and demand his release.

The mother, sister and brother-in-law of Amir Hekmati were in Washington this week, meeting State Department officials and members of Congress. Despite improvements in Hekmati’s detention conditions, they say he is “emaciated” after more than a year in solitary confinement and a month on hunger strike.

“Until the highest-level government officials in the U.S. make statements and request his release, I think it won’t have enough relevance,” sister Sarah Hekmati said.

Efforts in Iran to free the 29-year-old Iranian-American are at a standstill after more than 600 days of incarceration, the family said.

State Department spokesman Patrick Ventrell said Friday that freeing Hekmati is a top priority.

“We continue to have serious concerns about the fate of U.S. citizen Amir Hekmati,” Ventrell told reporters. “We are determined to secure his release and remain deeply concerned about his well-being in Iranian custody. Our diplomatic efforts to secure Mr. Hekmati’s release are ongoing.”

Iran accuses Hekmati of spying for the CIA. American officials deny the charge. But they have little influence with Iranian authorities, as Washington and Tehran haven’t had diplomatic relations for more than three decades.

Hekmati’s family says he went to Iran in 2011 to visit his grandmothers.

Hekmati was born in Arizona and grew up in Michigan, where his parents and sister still live, and carries U.S. and Iranian passports.

Recently, his fortunes have improved. He was transferred earlier this year to a less-restrictive environment after 16 months of solitary confinement. His death sentence was overturned. He was allowed to write a letter to his family. And authorities permitted an uncle in Iran to visit him.

The family is still hoping to sway Tehran on humanitarian grounds, with Hekmati’s father suffering from brain cancer.

“Every day he takes his chemo medication and always asks, ‘God, please bring my son back before I leave this life,’” said Behnaz Hekmati, Amir’s mother. Of her son, she said: “He’s the oldest son. We really need him. If something happens to us, he’s the one who can protect the family.”